Medical device delivery systems for self-expanding implants are generally advanced within a body of a patient along a desired vascular path or other body passageway, until the medical device within the catheter system is located at the treatment site. As a general matter, while watching the relative positions of the medical device and the catheter system components with respect to a stenosis on a video x-ray fluoroscopy screen, the physician holds the proximal hub attached to the inner shaft member in a fixed position with one hand, while simultaneously gently withdrawing the proximal hub attached to the outer tubular sheath with the other hand.
The deployment operation may require a measure of skill and experience. For example, among these reasons is the dynamic blood flow at the desired site for treatment, which may be further disrupted by the presence of a lesion or stenosis to be treated. Another factor is the gradual resilient expansion of a medical device as the outer sheath is retracted. This gradual expansion presents an opportunity for a “watermelon-seed” phenomenon to occur. This watermelon-seed effect may cause the resilient medical device to apply a force against the outer sheath, such that the self-expanding implant can move forward.
Thus, the physician may need to accurately hold the two proximal hubs in a desired specific arrangement and positioning, in which the hubs are properly held against the expansion force, while further attaining and maintaining accurate positioning of the medical device until it contacts the vessel. In a successful deployment and positioning of the medical device, the inner shaft of the delivery system should preferably be held stationary in the desired position. If the physician's hand that holds the inner shaft hub moves inadvertently during deployment, it is possible that the medical device may be deployed in a non-optimum position.
Also, the elongated inner and outer catheter shaft members may exhibit weakness which may present an opportunity for the position and movement of each proximal hub to differ from the position and movement of the respective distal ends of the inner and outer shaft members. Yet another factor is that the position of the medical device may be adjusted up until the point at which a portion of the expanding portion of the medical device touches the sidewalls of the body passage, so that the position of the medical device should preferably be carefully adjusted until immediately before a portion of the medical device touches the anatomy.
Some known catheter systems require two-handed operation, such as those with a pair of independent hubs, one hub on the inner and outer shaft member, respectively. Other known catheter systems include a pistol and trigger grip, with a single mode of deployment, involving a single trigger pull to deploy the associated medical device.
Accordingly, although physicians may be capable of operating such known systems with great skill, it is desirable to provide an improved catheter delivery system capable of facilitating easier and more accurate deployment and positioning of resiliently expansive medical device.
In addition, it is desirable to provide an advanced catheter deployment mechanism having two modes of operation. In the first mode of operation, the delivery mechanism preferably provides a precisely adjustable link between the inner and outer catheter shaft members, such that the relative position of the outer sheath with respect to the inner catheter shaft member can be precisely and selectively adjusted. Yet at any selected position, the delivery mechanism should preferably maintain this selected relative position of the inner and outer catheter shaft members, while resisting any force that may be present tending to move the inner or the outer catheter shaft members with respect to the other. In a second mode of operation, the delivery mechanism should preferably enable the physician to rapidly withdraw the outer tubular sheath with respect to the inner catheter shaft member preferably in a proximal direction with a single easy motion.